Yes that would be too great a risk. Just partitioning them differently increases the possibility of corruption although in theory it should be fine.
I tried this several years ago. Essentially I was trying to do the same thing that flyboyy seems to wwant to do. I discovered three things that made me abandon the idea.
1. At the time the only way I could think to keep both computers from trying to access the drive at the same time was to use some sort of usb switch with two inputs and one output and a switch to control which computer was giveen access to the drive. At the time I either could not find such a switch or they were expensive. I don't remember which was the case.
2. I found directions online whhich demonstrated how to format the drive in such a way that one partition was for Mac and one for PC. Some ussers reported data loss when they tested this configuration and others did not. Although I did not experience data loss in limmited testing, I din't really trust the drive for a data backup.
3. During testing I discovered that my Mac would mount the PC partition with no problems when it was connected to the Mac
but I had to jump through a hoop or two to get the Mac partition to mount. I don't thiink everyone had this problem.
In the end I decided this was more of a pain than it was worth. Took some time, and several failed ateempts, to set this up. After a while I was doing it mainly to see if the process was reliable/easy enough for a How To column I was writing.
